Another from Glengarry Glen Ross. Jack Lemmon cold calls a guy trying to sell real estate. Lemmon's use of little gestures, from flipping himself the bird to showing too much sock as he states how he isn't afraid of familiarity, are just masterful. Great use of the pouring rain at the end.

edit- After watching it again, I guess he didn't flip himself the bird. Still great.

I searched Youtube but couldn't find it. One of my all time favorites is from Gone With the Wind, when Rhett stares up the stairs at Scarlett for the first time. And Scarlett says he makes her feel like she's "got no drawers on!"